Epithelia form barriers that are essential to life. This is particularly true in oral and GI mucosal tissues that are constantly exposed to dietary and environmental antigens and the resident and foreign bacterial flora. For a barrier to exist, the intercellular space need be maintained and this is accomplished by the organization of the tight junction (TJ) complex. The multi-molecular TJ complex forms a belt at the apical portions of cells and is best divided into three groups: (i) integral TJ proteins that form strands which bridge the intercellular space and consist of proteins such as claudins, occludins, and junction adhesion molecules; (ii) cytoplasmic junctional molecules such as TJ proteins with PDZ domains i.e. zonula occludins (ZO-1, ZO-2, ZO-3); and (iii) the actin cytoskeleton. When assembled, TJs show ion and size selectivity for paracellular transport due to the presence of aqueous pores within paired TJ transmembrane proteins. The integrity of the TJ complex is dependent on connections between claudins and the actin cytoskeleton, which is largely mediated by PDZ domain-containing cytoplasmic proteins ZO-1, -2, and -3.
The mechanism by which amphiregulin (AR), an autocrine growth factor, regulates the barrier is not fully understood but the H2O2/TACE/EGFR ligand/EGFR signaling axis, also described as the “oxidant-induced metalloproteinase-dependent EGFR transactivation” pathway, was recently proposed (Forsyth, C. B., et al. J Pharmacol Exp Ther, 2007. 321(1):84-97). Putnins et al., using a rat periodontal disease model, identified increased EGFR signaling in diseased periodontal tissues (Firth, J. D., et al. J Clin Periodontol. 2013 40(1):8-17). Histological analysis of tissues from patients with inflammatory bowel diseases (IBD) e.g. Crohn's and ulcerative colitis have also shown AR expression primarily in the epithelium, whereas AR is absent in healthy patients (Nishimura, T., et al. Oncol Rep, 2008. 19(1):105-10).